In blood purification treatment, e.g., dialysis treatment, a blood circuit formed from flexible tubes is generally used to circulate the patient's blood extracorporeally. The blood circuit is formed primarily from an arterial blood circuit to which an arterial needle is attached to an end to collect blood from the patient and a venous blood circuit to which a venous needle is attached to an end to reintroduce blood to the patient. A dialyzer is interposed between the arterial blood circuit and the venous blood circuit to purify the extracorporeally circulated blood.
This dialyzer contains a plurality of hollow fibers. Blood flows through these hollow fibers while dialysate flows outside (between the outer perimeter surfaces of the hollow fibers and the inner perimeter surface of the case). The hollow fibers are formed with a plurality of micropores on its walls, and the waste products and the like of the blood flowing through the hollow fibers pass through a blood purification membrane and are discharged into the dialysate. The purified blood from which the waste products have been discharged is then reintroduced to the body of the patient. An ultrafiltration pump is provided to remove water from the patient's blood in the dialyzer so that ultrafiltration can be performed during dialysis treatment.
When, for example, extracorporeal circulation is performed by applying the arterial needle and the venous needle to a patient's shunt (an access vessel provided by a surgical operation that connects an artery and vein) and its vicinity, blood recirculation can take place, where the blood from the venous needle that has been purified and reintroduced to the patient's body can be reintroduced into the arterial needle without having passed through the patient's organs and the like. When this type of blood recirculation takes place, purified blood is further circulated extracorporeally, reducing the flow of extracorporeal circulation of blood that needs to be purified, leading to lower blood purification efficiency. Also, if blood recirculation takes place, a device for detecting the concentration of the extracorporeally circulating blood such as a blood volume measuring device (hematocrit sensor) will not provide values that reflect the blood concentration for the patient's whole body, preventing reliable data from being obtained.
Accordingly, as described in JP2001-502590 (a Published Japanese Translation of a PCT Application), a conventional hemodialysis apparatus has been proposed wherein an indicator in the form of a concentration agglomeration is applied to the extracorporeally circulating blood suddenly and in a short period of time. This indicator (concentration agglomeration) is detected, and the area ratio of the detection signal indicating the change in blood concentration of the obtained indicator is used to calculate a recirculation rate. With the hemodialysis apparatus described in this document, a recirculation rate can be measured in a short period of time.